1. Field of the Invention
The field of the invention is that of resonant cavity devices.
2. Description of the Prior Art
Some resonant cavity devices comprise a waveguide body having a lateral wall extending in a longitudinal direction and delimiting at least one resonant cavity with two opposite end walls.
To limit the weight of such devices in onboard applications, especially in aeronautics, it is particularly advantageous to fabricate them from aluminum.
The person skilled in the art knows that if such devices are coupled to equipment such as multiplexers, for example output multiplexers (Omux), they are subjected to frequent temperature variations, especially if the power of the signals that they receive increases strongly. However, this also occurs in so-called “outband” operation, i.e. if the received signals have a frequency slightly outside the band of frequencies in which they are intended to function. Consequently, if the resonant cavity is delimited by aluminum walls (with a high coefficient of thermal expansion), in the presence of temperature variations it is subject to dimensional variations that induce a frequency offset of its band of frequencies.
Various solutions to this problem have been proposed.
A first solution consists in using an aluminum device and interrupting its operation if its temperature exceeds a set threshold. This avoids having to uprate the multiplexer to tolerate outband operation. However, it necessitates coupling the resonant cavity device to a thermal control device.
A second solution also consists in using an aluminum device and equipping it with a heat evacuation device, for example braids. However, this solution proves to be unsuitable if the resonant cavity device must simultaneously withstand high power levels and high interface temperatures. Furthermore, this solution leads to a weight penalty.
A third solution consists in using a device whose walls are made from a material having a very low coefficient of thermal expansion over a wide range of temperatures, for example the nickel-steel alloy known as Invar®. However, although these materials have a beneficial coefficient of thermal expansion, they do not generally offer light weight and/or low cost and/or good thermal conductivity. Moreover, resonant cavity devices made entirely of Invar® have already reached their limits in terms of power and interface temperature (because the coefficient of thermal expansion (CTE) of Invar® is not zero).
A fourth solution consists in using an aluminum device and adapting at least one of its end walls, for example as in devices described in the documents U.S. Pat. No. 6,002,310 and EP 1187247. To be more precise, the device described in the document U.S. Pat. No. 6,002,310 comprises an end wall equipped with an Invar® first wall, the central portion of which has been made thinner, and a protuberant aluminum second wall fastened to the thick peripheral edge of the first end wall. If the temperature varies, the central portion of the protuberant second wall expands, which makes it more protuberant, and constrains the Invar® first wall to flex, thereby amplifying the protuberance phenomenon. The device described in the document EP 1187247 constitutes a substantially equivalent solution. The correction of dimensional variations in the devices described in the above two documents is of limited extent, which limits the power and the interface temperature of the Omux to which they are coupled.
Thus none of the prior art devices is entirely satisfactory.
Thus an object of the invention is to improve on this situation.